A. Technical Field
The present invention relates to an admixture for cement, a polycarboxylic acid-based polymer for an admixture for cement, and a producing method thereof, and a cement composition. More particularly, the present invention relates to an admixture for cement excellent in slump retaining performance, which enhances flowability, and retains the flowability with time, in a so-called cement composition such as a cement paste, a mortar and a concrete, and a polycarboxylic acid-based polymer for an admixture for cement suitable therefor, and a producing method thereof, and a cement composition.
B. Background Art
Since a cement composition (also referred to as cement blend) gives a hardened cement excellent in a strength and durability, it is widely used in utility such as a building outer wall material and a building structure. Examples of such the cement composition include a cement paste obtained by adding water to a cement, a mortar obtained by mixing therein a sand which is a fine aggregate, and a concrete obtained by further mixing therewith a small stone which is a coarse aggregate and, usually, in order to enhance air-entraining property and flowability, an admixture for cement is added and, in recent years, its importance has been recognized, and technological innovation is being performed vigorously.
A role of an admixture for cement is to exert sufficient dispersibility to maintain its flowability and execution property even when water in a cement composition is decreased, realize improvement in durability and a strength due to water reduction and, at the same time, retain stable dispersibility with time to acquire a better cement composition. And, in the recent concrete art, a concrete which realizes such the performance is strongly required and, in order to attain this, reduction in a unit water amount and prevention of reduction in flowability are an important theme.
Among various admixture for cements, in particular, a polycarboxylic acid-based cement dispersant is advantageous as compared with other cement dispersants such as a naphthalene-based cement dispersant in that it exerts high dispersing performance and, as such the cement dispersant, a cement dispersant containing a copolymer consisting of a specified unsaturated polyalkylene glycol-based monomer and a (meth)acrylic acid-based monomer has been proposed (for example, see JP-A No. 9-86990).
However, these polycarboxylic acid-based cement dispersants have not completely overcome reduction in dispersing performance due to passage of a time yet and, further, in a high water reduction rate region necessary for a high strength concrete, there arises a problem such as reduction in workability of a concrete composition. That is, under current circumstances, in a high water reduction rate region, flowability of a concrete is reduced, a viscosity becomes high particularly under high shear, a pump load at pumping under pressure becomes extremely large, and harmful influence is caused in pumping under pressure. In particular, when an air temperature is 15° C. or lower in winter, a temperature of a concrete is reduced like an air temperature, a viscosity of a concrete becomes high, workability is remarkably reduced, initial dispersibility of a cement dispersant is reduced, and filling property into a mold is deteriorated, resulting in remarkable damage of workability. As a method of retaining flowability, that is, preventing reduction in slump, there is an example in which improvement was tried paying attention to a length of a polyalkylene chain (for example, see JP-A No. 9-286645), but a use amount tends to increase, and an admixture for cement which is used at a small amount, and retains flowability for a long term is highly desired.